1. Field of the Invention
The present invention relates to disk apparatuses and, more specifically, to disk apparatuses which write information to a disk-shaped recording medium and/or read information therefrom by using an optical head while rotating the disk-shaped recording medium.
2. Description of the Related Art
A conventional disk apparatus, which is specifically a CD-ROM apparatus, will be hereinafter described. FIG. 6 is a plan view of a CD-ROM apparatus that was proposed by the present assignee in Japanese Unexamined Patent Publication No. Hei. 7-254202. FIG. 7 is a partial sectional view taken along line VI--VI in FIG. 6. FIG. 8 is a sectional view of a 120-mm-diameter CD-ROM disk (hereinafter referred to simply as "disk") that is used in the CD-ROM apparatus concerned.
A disk 30 is shaped such that a 15-mm-diameter opening 30a is formed at a central portion of a 120-mm-diameter circular plate. An area from the perimeter of the opening 30a to a 50-mm-diameter circle is a non-recording area 30b, and an area from the 50-mm-diameter circle to a 116-mm-diameter circle is a recording area 30c. In the non-recording area 30b, an area from the 15-mm-diameter circle to a 33-mm-diameter circle is a clamping area 30d that is used for a CD-ROM apparatus 1 to support the disk 30.
The CD-ROM apparatus 1 is generally composed of a chassis assembly 2 and a movable assembly 3 that is held by the chassis assembly 2 so as to be movable in directions X1 and X2. The movable assembly 3 is provided with a disk supporting and rotating means 4 for supporting and rotating the disk 30 which means is composed of a rotor unit 4a and a stator unit 4b. The movable assembly 3 further includes an optical head 5 for reading information from the disk 30, and an optical head moving means 6 for moving the optical head 5 in the radial direction of the disk 30.
The disk supporting and rotating means 4 has a configuration including a known radial-gap-type spindle motor. The rotor unit 4a has a rotary shaft 7, a case body 8, a turn table 9, and an annular rotor magnet 10. The stator unit 4b has a bearing unit 11, and a stator coil 14 that is constituted of a core 12 and a winding 13 that is wound on the core 12. In the spindle motor, when the stator coil 14 is energized while being controlled by a rotation control means (not shown), it exerts magnetic drive force on the rotor magnet 10, so that the rotor unit 4a is rotated.
The case body 8 and the turn table 9 are integral with each other and fixed to the rotary shaft 7. A disk support portion 9a of the turn table 9, which portion is about 15 mm in radius, supports the disk 30 while contacting with its clamping area 30d. A rotor magnet accommodating portion 8a of the case body 8, which portion is about 13 mm in radius, accommodates the annular rotor magnet 10.
The optical head 5 is required that a lens portion 5a be movable to a location that is opposed to the inner border of the recording area 30c of the disk 30 which border is 25-mm apart from the rotation center of the disk 30. On the other hand, to prevent an end 5b of the optical head 5 on the side of the disk supporting and rotating means 4 from contacting the rotor unit 4a of the means 4, the outer dimensions of the optical head 5 should be such that the distance from the lens portion 5a to the end 5b is shorter than about 12 mm, which is the distance 25 mm from the disk rotation center to the lens portion 5a minus the radius 13 mm of the rotor unit 4a.
In the disk apparatus 1, as shown in FIG. 7, the rotor magnet accommodating portion 8a of the disk supporting and rotating means 4 and the optical head 5 are located side by side in the disk radial direction. Therefore, the dimensions and the shape of each of the disk supporting and rotating means 4 and the optical head 5 are so restricted as to avoid interference therebetween.
That is, the radius p of the rotor magnet accommodating portion 8a of the rotor unit 8 and the distance q between the lens portion 5a and the end 5b of the optical head 5 should satisfy a relationship EQU p+q&lt;25 mm.
As for the disk supporting and rotating means 4, the diameter of the rotor unit 4a cannot be made large because of the limitation on the diameter of the rotor magnet 10. Therefore, the moment of the magnetic drive force of the disk supporting and rotating means 4 is relatively small, which is disadvantageous in increasing the rotation speed. In particular, in thinner CD-ROM apparatuses (for notebook-type computers) which should employ a 5-V drive voltage, the moment of the magnetic drive force is insufficient and it takes 2 to 5 seconds to complete a CLV track search. Thus, the desired data transfer rate of 6-fold/8-fold speed is not attained. Further, in quadruple-speed CD-ROM apparatuses, the necessary rotation speed is attained by employing a 12-V drive voltage because it cannot be attained by a 5-V drive voltage, which is employed in double-speed CD-ROM apparatuses. However, the increased drive voltage causes a problem of a large power consumption. The increased drive voltage also increases the amount of generated heat and, hence, requires a stronger cooling means than in the previous cases. This is disadvantageous in reducing the size and the cost of the apparatus.
As for the optical head 5, it is difficult to design the inside structure because the distance q between the lens portion 5a and the end 5b is so restricted that the optical head 5 does not interfere with the disk supporting and rotating means 4 when the lens portion 5a is moved to be opposed to the inner periphery of the disk 30. This problem is remarkable in optical heads capable of writing, such as an optical head of a CD-R apparatus.